This invention relates generally to a data packing control for message transmission and, in particular, to the compaction of graphic data by run length encoding using control digits for image reproduction.
1. Field of the Invention
In a facsimile communication system, images comprising black characters on a white background are usually transmitted to a reproducing system such as a cathode ray tube, light emitting diodes or such display device, or a dot printer such as an ink jet or wire printer. Generally, the scanned data is encoded into a compressed form before data transmission to permit faster transmission to the display reproduction device. At the receiver end, a suitable decompression scheme is used to recover the original data.
To obtain a high quality reproduction of the original characters, generally a fine scan device and a fine reproduction device are used. Thus, for high quality reproduction, the characters are generally scanned at, for instance, 720 picture elements per inch and reproduced at the same picture element rate. This produces a very good reproduction of the original character. However, this high number of picture elements at the scanning device forces the storage of many bits of information even with compression schemes since many picture elements must still be converted to a binary data information for transmission.
In order to decrease the scanning and storage complexity, the characters were generally scanned at a coarse scanning rate of, for instance, 180 picture elements per inch and printed or reproduced at the same coarse level. At this coarse scan level, less memory storage and lower data rate transmission can be used. However, the print quality is low and includes a large number of noticeable staircases that are unacceptable to an observer.
It is, therefore, an important object of the present invention to provide a process for the transmission of character data that includes the compaction of the graphic data in combination with grey level representation that permits the use of a coarse scanning device together with a fine reproduction device to accomplish an enhanced character scan transmission and reproduction.
2. Description of the Prior Art
It is known that compaction of graphic data can be accomplished by using run-length encoding with binary numbers corresponding to various blocks of data while using characterized control digits to switch between the black and the white background information. U.S. Pat. Nos. 3,483,317 to DeGroat and 3,643,019 to Beltz disclose such systems. The DeGroat Patent teaches the use of control digits to switch from run length coded data to black and white data information for reproduction. The Beltz Patent teaches the use of a number of bytes in a pattern as being dependent on the length of the segments. One bit determines the beginning and end of the segments. However, no known prior art teaches the combination of the compaction of graphic data while using a control digit to switch between character and background information in combination with a representation of the grey level values for the graphic character representation.
Another object of the present invention, therefore, is to provide an enhanced data compaction scheme that includes a grey level representation.
Further, the prior art character scanning, transmission and reproduction schemes permitted only a coarse reproduction of coarsely scanned data or, if a better quality reproduction was desired, a fine reproduction of a finely scanned character. There is no showing in the prior art of the use of a data compaction scheme that permits the high quality fine reproduction device of a coarsely scanned signal that includes graphic data compaction with a grey level representation that can be decompressed and decoded to permit the fine high quality reproduction with very little loss of resolution.
Yet another object of the present invention, therefore, is to provide a character reproduction process that provides a fine reproduction from a coarse scan.